Process for producing p-xylylene-containing compositions



United States Patent 3,280,202 PROCESS FOR PRODUCING p-XYLYLENE- CONTAINING COMPOSITIONS Heinrich G. Gilch, Plainfield, N..l., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed July 9, 1964, Ser. No. 381,565 16 Claims. (Cl. 260-648) This invention relates to a new and improved process for producing precursors from which may be obtained such compounds as p-xylylenes, poly(p-xylylenes) and/or cyclo (di-p-xylylenes).

Heretofore, these p-xylylene, poly(p-xylylene) and/or cyclo(di p xylylene) compounds have been obtained through pyrolytic processes which were directed to the decomposition of compounds having the general structure wherein R is an alkyl group having from about 1-6 carbon atoms. In order to be effective, however, this pyrolysis required extremely high temperatures in the order of about 800 0-1000 C. At these extremely high temperatures, great difiiculty has been encountered in controlling the reaction, controlling the rate of the reaction and avoiding interference from side reactions. Furthermore, only relatively low yields of final products have been realized since much of the starting material is destroyed by decomposition and charring of the reactive intermediary compounds formed during the reaction. Utilization of these pyrolytic processes have also limited the type and variety of starting materials which may be employed. For example, hexachloro-p-xylene can not be polymerized by pyrolysis since it prematurely decomposes at the high temperatures employed resulting in only a tar-like substance.

Pyrolytic processes are, therefore, undesirable as a means for obtaining p-xylylenes, poly(p-xylylenes) and/ or cyclo(di-p-xylylenes) since they are, generally, uneconomical and are not commercially feasible.

Solution processes have also been employed to obtain poly(p-xylylenes). These processes are also undesirable since the poly(p-xylylenes) recovered are generally powdery in form, insoluble in well-known solvents, and infusible. Hence, they are subjected to further processing only with extreme difliculty.

It is an object of this invention, therefore, to provide a process whereby precursors for the production of p-xylyle-nes, poly(p-xylylenes) and/or cyclo(di-p-Xylylenes) may be commercially and economically obtained.

It is another object of this invention to provide a process which will result in relatively greater yields of precursors from which greater amounts of p-xylylene, poly(p-xylylene) and/ or cyclo(cli-p-xylylene) compounds are obtained.

Another object of this invention is to provide a process whereby poly (p-xylylenes) are obtained in desired, usable forms.

A further object of this invention is to provide a process which utilizes lower temperatures than have been heretofore realizable in obtaining p-xylylenes, poly(p-xylylenes) and/ or cyclo (di-p-xylylenes).

A still further object of this invention is to provide a process which enables one to utilize a great variety of starting materials to produce the precursors from which p-xylylene, poly(p-xylylene) and/or cyclo(di-p-xylylene) compounds are obtained.

Yet another object of this invention is to provide a process for producing precursors which is readily controllable and which minimizes interference from side reactions.

These and further objects will become apparent from the ensuing discussion.

ice

Now, in accordance with the instant invention, it has been found that greatly increased quantities of p-xylylene precursors can be economically and readily prepared from which commercial amounts of p-xylylene-containing compositions, i.e., p-xylylenes, poly(p-xylylenes) and cyclo(dip-xylylenes) are obtained. This result is made possible through the process of the instant invention wherein a compound is heated to a temperature of between about 400 C.0 C. in contact with a metal reducing agent, said compound having the general structure X Yzo OY2 I Z wherein Y is a member selected from the group consisting of halogens, hydrogen, or mixtures thereof, X is a member selected from the group consisting of halogens having a. bond strength no greater than that of Y, Z is a member selected from the group consisting of hydrogen and halogens having a bond strength no greater than that of Y and n is an integer from 1 to 2, inclusive, with the proviso that when n has a value of 2, Y is a. member selected from the group consisting of all halogens and all hydrogen. This process yields 'highly increased quantities of reactive intermediary pxylylene precursors having the general structure YzC= =CY2 wherein Y is a member selected from the group consisting of halogens, hydrogen and mixtures thereof. Once the reactive intermediary p-xylylene precursors are formed, well-known condensation techniques may be employed to obtain either p-xylylenes or poly(p-xylylenes) and/or cyclo(di-p-xylylenes).

It can be readily seen, therefore, that a great variety of starting materials can be employed in the instant invention. The term starting materials is intended to include all compounds which correspond to compounds having the general structure wherein Y, X, Z and n are as described hereinabove.

Thus, it is possible to employ a-rnonohalo-p-xylenes as starting materials; that is, compounds having the structure wherein X is a member selected from the group consisting of halogens and n has a value of either 1 or 2. When n has a value of 1, these compounds may also be termed a-halogenated p-xylenes. When n has a value of 2, these compounds are properly termed 1,2-a-halo-bis-(p-tolyl)- ethanes.

Similarly, it is also possible to employ fully substituted starting materials; that is, compounds wherein the Y, X and Z constituents are all halogens. However, when Y is a halogen in the compound having the general structure X and Z can also be halogens having an equal or lower bond strength than Y. Thus, if Y is chlorine, X and Z can also be chlorine or a halogen having a lower bond strength than ch1orine; such as, either bromine or iodine.

The term bond strength, as employed herein is intended to mean that quantity of energy required to break the covalent bond existing between the carbon atom and the halogen or hydrogen atom in the on position of the starting compounds.

Similarly, the term fully substituted, as employed herein, is understood to mean full replacement of the hy- 3 drogen atoms in the OL-pOSllllOHS of the starting material with another constitutent, such as a halogen. The term partial substitution would, therefore, be understood to mean that less than all of these hydrogen atoms are thusly substituted.

Other starting compounds can also be employed wherein one Y constituent is hydrogen and the other a halogen. In these instances, X can be any halogen having an equal or lower 'bond strength than Y and Z may be either hydrogen or any halogen having an equal or lower bond strength than Y. If Z is a halogen under these conditions, it need not be the same halogen as is employed in the X position but need only be a halogen having a lower bond strength than the halogen employed in one of the Y positions. However, Where one Y constituent is hydrogen and the other a halogen, n can only have a value of 1. When n has a value of 2, the Y constituent must be all hydrogen or all halogen. This proviso is necessary in order to properly form the reactive intermediary p-xylylene precursors and thus permit optimum control over the process reaction so as to insure that only the X and/or Z constituents are alfected by the metal reducing agent.

While the Y, X and Z constituents in the compound having the general structure wherein n is as above, have been discussed as being comprised of either hydrogen or halogens, it should be understood that other elements and compounds may also be employed, particularly in the X and/ or Z positions. Hence, constituents comprised of cyanide compounds, sulfur compounds and so forth may also be employed. However, care should be exercised in selecting these constituents since, in the process of this invention, these constituents react with the metal reducing agent to form a compound which must be isolated from the process in order to obtain optimum results.

Generally, the compounds formed upon reacting with the metal reducing agents should be volatile and easily sublimable when subjected to the reaction conditions of the instant process. If the compounds formed are not volatile and, thereby, not easily sublimable, it has been found that they will form and deposit directly on the reducing agent. This coating seriously impairs and hampers the reaction and will, ultimately, cause the reaction to halt, In the practice of this invention, it is preferred, therefore, to employ halogens in the X and/ or Z positions. It has been found that halogens readily form halide compounds with the metal reducing agents employed which compounds are volatile and can be easily sublimed. These compounds may then be readily isolated from the reaction system permitting the process to continue unimpaired to completion.

It has been further found that halogens have a greater tendency to form these compounds than do other constituents. This, in turn, greatly enhances the formation of the reactive intermediary p-Xylylene precursors and also contributes to their increased yield.

In accordance with the instant invention, merely heating the starting compounds in contact with a metal reducing agent, to temperatures of between about 400800 C. will yield reactive intermediary p-xylylenes. Hence, the instant process avoids all the limitations inherent and encountered in pyrolytic processes. In pyrolytic processes the constituents in the OL-POSllllOHS of compounds having the general structure wherein Y, X, Z and n are as above, are homolytically cleaved to form reactive intermediary p-xylylenes. This cleaving results directly from the extremely high temperatures utilized and required in pyrolysis. By employing metal reducing agents in the process of the instant invention, with which the starting compounds are contacted, significantly lower temperatures can be employed which results in an entirely different reaction.

Although temperatures below 400 C. may be employed, this is not desirable since there is less conversion of the starting compound into the reactive intermediary p-Xylylenes. In like manner, temperatures above 800 C. may be employed but this also will result in decreased yields of the p-xylylene precursors due to decomposition of the starting material. Hence, for good results, the temperature employed should be between about 400 C. 800 C. and preferably between about 500 C.-700 C.

Controlling the pressure in the system of the instant process may also be desirable. The pressure in the system of the instant process may be conveniently measured by well known means at the outlet end of the reaction chamber. Henceforth, any [further reference to pressure .is intended to mean that pressure which is measured at the outlet end of the reaction chamber in the instant process. Generally, low partial pressures may be employed in the instant process of betwen about 0.01 mm. Hg10.0 mm. Hg and preferably between about 0.05 mm. Hg-0.5 mm. Hg. Although partial pressures below a 0.01 mm. Hg and above 10.0 mm. Hg may be tolerated, resulting yields of the reactive intermediary p-Xylylenes will be decreased in the same manner as when low or very high temperatures are employed.

It is also possible to employ inert vaporous diluents in the instant process in order to further reduce the partial pressure of the reactants and thereby make it possible to operate at high total pressures without destroying the maximum yields of reactive intermediary p-xylylenes obtainable. As an inert diluent, steam is particularly desirable since it has an added advantage of producing a protective effect by preventing decomposition or charring of the reactive intermediary p-xylylenes when the reaction is conducted at or near the higher temperature ranges. In addition to steam, other inert diluents, such as nitrogen, argon and like inert gases, can also be employed.

Thus, the total pressure in the system will depend upon the operating partial pressures desired and the amount of steam or other inert diluent employed. Hence, it is possible to operate in this process at total pressures, even up to atmospheric pressure or higher.

The amount of inert diluent present is not narrowly critical but, when employed it should be present, generally, in an amount of between about 40:1 to 130:1 parts by weight of inert diluent to starting material, respectively, and, preferably, in an amount of between about 9021 to :1 parts by weight of inert diluent to starting material, respectively, although excess diluent is not detrimental to the process.

When the starting compounds are brought into contact with the metal reducing agent present in the preheated reaction chamber, the halogen constituents in the ot-positions of these compounds are reduced by the reducing agent and thereby form the reactive intermediary p-xylylenes. Generally, the reducing agents which may be employed are those which will effectively reduce halides and are capable of remaining volatile in their reacted state; such as copper, zinc, aluminum, tin, and the like. In the practice of this invention, copper is a particularly preferred reducing agent since the cuprous halide compounds which are formed have been found to be volatile and sublime readily. This permits them to be easily isolated from the reaction thereby permitting the process to continue without interference or loss due to side reactions. While the amount of reducing agent employed is not critical, a suflicient amount should be present in the reaction chamber to assure that all of the starting material is reacted. In order to obtain best results, the amount of reducing agent should be present in stoichiometric excess to the amount of starting material employed.

The physical form in which the reducing agent may be present is also not critical. Generally, the reducing agent should be in a form which permits the greatest possible surface area of the reducing agent to be exposed. On the other hand, the reducing agent should not be inserted in the reaction chamber in such a manner as to produce a severe pressure drop between the inlet and outlet ends of the reaction chamber. Usually, the reducing agent can be present in the form of a mesh, small particles, strips, shavings and so forth. However, it has been found that when the reducing agent is in mesh form and is loosely packed in the reaction chamber, good results are obtained and this form is preferred.

When halogens are the constituents in the Ot-POSltlOI'lS of the starting compounds, they are reduced upon contacting the reducing agent to form a halide compound. For example, when copper is employed as the reducing agent, a cuprous halide compound is formed. These halide compounds are in the form of vapors as they leave the reaction chamber. In order to avoid complicity with possible side reactions, assure optimum control over the process reaction and obtain maximum results, it is desirable that these vaporous halide compounds first be isolated from the hot vapors of the reactive intermediary p-xylylenes. This may be conveniently accomplished by simply permitting the vaporous halide compound to deposit on a relatively cool surface. Caution should be exercised, however, that the cool surface employed is maintained at a temperature which is above the condensation temperature of the vaporous reactive intermediary p-xylylenes which are formed. Generally, the cool surface should be maintained at temperatures of between about 150 C.-350 C. and preferably between about 250 C.-300 C. When the hot vapors are passed over this relatively cool surface, the vaporous, cuprous halide compounds deposit spontaneously on the surface while the reactive intermediary p-xylylene vapors pass over the surface unaffected by the reduced temperature.

Once the halide compounds have been thus isolated, the hot vaporous reactive intermediary p-xylylenes may now be condensed, in accordance with well known methods, to obtain either p-xylylenes, poly(p-xylylenes) or cyclo di-p-xylylenes).

Generally, the condensation techniques employed are those whereby the :hot, vaporous reactive intermediary p-xylylenes are cooled to temperatures below that of their condensation ceiling by depositing these vapors on a relatively cold surface; that is, a surface which is maintained at or about room temperature, or by passing them into suitable quench solvents. The condensation techniques employed will depend, in part, on the ease and convenience with which the desired end product is obtained.

For example, when p-xylylenes are the product desired, they may be readily obtained by passing the hot, vaporous reactive intermediary p-xylylenes having the general structure Y2C= =o Y2 70" C. to 80 C., such as toluene, hexane and the like.

Similarly, the inert atmosphere employed may be selected from any inert gas which is capable of being cooled to temperatures of about 40 C., and preferably between about 70 C. to C. For example, any of the noble gases may be suitably employed as the inert atmosphere.

The manner in which p-xylylenes are obtained in accordance with the process of the instant invention is set forth in Example I below. While this example is illustrative of the process of the instant invention, it should be understood that it, as well as the remaining examples set forth and referred to hereinafter, is not intended to be limitative thereof. Unless otherwise specified all parts are by weight.

EXAMPLE I Preparation of c r,a,utetrachlo ro p-xylylene Over a period of two hours, 55.1 grams of ot-hexachloro-p-xylene was passed through a reaction chamber. The reaction chamber was packed with copper mesh and maintained at a temperature of 500 C. The system was maintained at a pressure of 0.1-0.05 mm. Hg. The cuprous chloride compound which formed was collected in a glass tube which was connected, at one end, to the outlet end of the reaction chamber, while the other end led into a quench bath. The cuprous chloride compound was collected and isolated from the hot reactive intermediary p-xylylene vapors emanating from the reaction chamber by depositing the cuprous chloride on the surface of the glass tube which was maintained at a temperature of about 250 C. by means of an electric heating tape. The remaining hot vapors of the reactive intermediary p-xylylene derivative were passed into a quench bath which consisted of 1150 ml. of toluene which was maintained at a temperature of 78 C. The quench bath was rapidly stirred by means of a magnetic stirrer. A yellow colored suspension formed and was filtered under an atmosphere of argon which was maintained at 78 C. The filtrate Was washed with cold ether in order to remove any impurities that may have been formed by side reactions. The product was then dissolved in tetrahydrofuran which was maintained at a temperature of 10 C. The solution was treated with charcoal and again filtered to insure that all impurities were removed and then slowly cooled to 78 C. Yellow, needle-shaped crystals were formed which were isolated by filtration and washed again with ether in order to remove the mother liquor. The remaining crystals were dried in vacuum at a temperature of 78 C. to yield 26.2 grams of a,a,a',a'tetrachloro-p-xylylene.

A small portion of the product was heated and was found to polymerize, practically quantitatively, to form poly-a,ot,a',u'-(tetrachloro-p-xylylene). Results of elemental analysis of the polymer are as follows.

Calculated: 39.67% C; 1.65% H; 58.68% Cl. Found: 39.80% C; 1.66% H; 58.04% C1.

Examples II and III below are set forth in order to establish not only that a,a,u',oz'-tetrachloro-p-xylylene was obtained according to the process of Example I but, further, that the reactive intermediary p-xylylene vapors can be further reacted to form additional compounds.

EXAMPLE II A solution consisting of 0.5 grams of a,a,ot',a-tetrachloro-p-xylylene in carbon tetrachloride was reacted with a solution consisting of carbon tetrachloride and bromine to yield 0.7 grams of a crystalline solid upon recrystallization from heptane. The crystalline solid had a melting point of C.-131 C. and was identified by elemental analysis, infrared spectrum and nuclear magnetic resonance spectrum as a,a'dibrom-o-ot,ot,a,ot-tetrachloro-pxylene. Its elemental analysis was as follows.

Calculated: 23.88% C; 0.99% H; 35.32% Cl; 39.80% Br. Found: 24.06% C; 0.99% H; 35.33% Cl; 39.45% Br.

'2 EXAMPLE III A sample of a,a,a,a-tetrach1oro-p-xylylene was reacted -with nitrogen dioxide by bubbling nitrogen dioxide through a solution consisting of 0.9 gram of a,a,ot',ot'-

tetrachloro-p-xylylene in carbon tetrachloride. The solution was maintained at a temperature of 10 C. When the solution was concentrated, a crystalline compound formed which was isolated after recrystallization from heptane. The amount of crystalline compound recovered was 0.6 gram and had a melting point of 95 C. Its elemental analysis, as calculated for u,a-dinitro-a,a,a',atetrachloro-p-xylene, was as follows:

Calculated: 28.74% C; 1.20% H; 42.51% Cl; 8.38% N; 19.16% molecular weight, 334. Found: 29.12% C; 1.05% H; 42.11% Cl; 8.45% N; 19.04% 0; molecular weight, 331.

The molecular weight was determined in dioxane by freezing-point depression.

When the compound was heated to about 105 C. or was permitted to stand at room temperature for several weeks, its melting point changed to 103 C.

The following example is set forth in order to illustrate the manner in which poly(a-halo-p-Xylylenes) may be ob tained from a-halo-p-xy-lylenes.

EXAMPLE IV Preparation of poly(a-tetrachloro-p-xylylene) from a,a,a',a-tetrachloro-p-xyZylene Into 400 ml. of tetrahydrofuran was dissolved 2.68 grams of a,a,a',a'-tetrachloro-p-xylylene obtained in accordance with the process of Example 1 above. The homogeneous solution was then divided into ten equal portions consisting of 30 ml. each. Each portion was maintained at a temperature of 20 C. in order to permit polymerization to proceed.

The polymerization process was interrupted periodically by rapidly cooling the solution to 78 C. Upon cooling, a suspension was obtained as in Example I above. This suspension was then filtered, washed in tetrahydrofuran and dried in vacuum at a temperature of 50 C. The amount of poly(a,a,a',a-tetrachloro-p-xylylene) recovered after various time intervals is set forth in Table A below:

TABLE A Time elapsed (in POly(cr,a,a',cz'-tetlilminutes) chlorn-p-xylylene) recovered (in mg.)

The same general process as described hereinabove may be similarly employed to obtain poly(p-xylylenes). This is accomplished when a starting compound having the general structure wherein Y, X, Z and n are as described hereinabove, is heated, in contact with a metal reducing agent, to temperatures of between about 400 0-800 C. to obtain reactive intermediary p-xylylenes having the general struc wherein Y is as above.

Once the reactive intermediary p-xylylenes have been formed, poly(p-xylylenes) may be conveniently obtained therefrom by condensing the reactive intermediary p-xylylenes on a cool surface; that is, a surface which is maintained at a temperature below the condensation temperature of the reactive intermediary p-xylylenes.

The manner in which poly(p-xylylenes) may be obtained in accordance with the process of the instant invention is illustrated by Examples VXI which are set forth below. Unless otherwise specified, all parts are by weight.

EXAMPLE V Preparation of poly a,a,a',a-tetrach loro-p-xyly lene) Several samples of commercially obtained a-hexachlorop-xylene were introduced into a reaction chamber. The reaction chamber was first packed with copper mesh in stoichiometric excess to the a-hexachloro-p-Xylene and then heated to maintain a temperature of between 300 C. and 600 C. The pressure of the system was maintained between 0.50.1 mm. Hg. A glass take-off tube, which was conected to the outlet end of the reaction chamber, was maintained at a temperature of about 250 C. by means of an electric heating tape. At this temperature, cuprous halide was collected on the walls of the glass takeoff tube while the remaining hot reactive intermediary p-xylylene vapors continued through the tube and were deposited at the cool end of the tube which was at about room temperature. The material deposited at the cool end of the glass tube was mechanically stripped off the tube. Infrared spectrum and elemental analyses showed it to be consistent with the structure of poly(a,a,a,a'- tetrachloro-p-xylylene). The elemental analysis was as follows.

Found: 39.80% C, 1.66% H, 58,21% Cl. 39.67% C, 1.65% H, 58.68% C1.

The yields of poly(a,a,a',a'-tetrachloro-p-xylylene) which were obtained by this process at various temperatures and pressures are set forth in Table B below.

Calculated:

TAB LE B Percent yield of poly Pressure Temperature, (oz,a,a',oz-tetlflchl0l0 (mm. Hg) C. p-xylylene) Recovered EXAMPLE VI Preparation of poly (oc-brOfflO-[J-X) lylene) and poly (p-xylylene) A 2.0 gram sample of commercially obtained m id-dibromo-p-xylene was introduced into a reaction chamber. The reaction chamber was first packed with copper mesh in stoichiometric excess to the a,adibromo-p-xylene and then heated to maintain a temperature of 450 C. The pressure was maintained at between 05-005 mm. Hg. The same procedure was then followed as in Example V above except that the hot reactive intermediary p-xylylene vapors were deposited in a gas chamber which was maintained at room temperature.

At the entrance to the deposition chamber, films of polyW-bromo-p-xylylene), copolymers of a-bromo-pxylylene and unsubstituted p-xylylene were deposited. At points further removed from the entrance to the chamber; that is, at points intermediary its length and near its outlet end, pure poly-(p-xylylene) was deposited.

The deposits were then mechanically stripped from the deposition chamber and the amount of polymers recovered was calculated to be about 60% by weight of starting material. Of the recovered amount, there was obtained 20% of poly(a-bromo-p-xylylene) and 40% poly(p-xylylene).

The deposition of these polymers at room temperatures is spontaneous. The manner in which they deposit is due to their respective molecular weights. Hence, those polymers having high molecular weights, such as poly(u-bromo-p-xylylene), will deposit first while those having low molecular weights, such as unsubstituted poly- (p-xylylene) will deposit last.

By regulating the temperature in the deposition chamber so that a substantially higher temperature is maintained at its entrance than is maintained at its outlet end, the amount of copolymers deposited can be materially decreased so that significantly increased amounts of polyW-bromo-p-xylylene) and unsubstituted poly(pxylylene) can be obtained.

EXAMPLE VII Preparation of ply(a-chlor0-p-xylylene) and poly(p-xylylene) The same procedure was followed as in Example VI except that the reaction chamber was maintained at a temperature of 550 C. a,a'-Dichloro-p-xylene was introduced into the reaction chamber which ultimately yielded 50% by weight of starting material of poly(uchloro-p-xylylene). As in Example VI above, there was also deposited, at the extreme end of the deposition chamber, unsubstituted poly(p-xylylene) in an amount of by weight of starting material.

The following examples are set forth in order to illustrate that unsubstituted poly(p-xylylenes) can be obtained in accordance with the instant invention when a halogen is substituted in only one oc-POSltiOIl in a methyl group of a p-xylene.

EXAMPLES VIII-XI Preparation of p0ly(p-xylylene) The same procedure was followed as in Example V above except that a-monochloro-p-xylene was introduced into the reaction chamber. The temperature of the reaction chamber was maintained by placing it inside a copper tube which was heated by an electric furnace. Control conditions and the amount of poly(p-xylylene) recovered, in percent by weight of the amount of ozmonochloro-p-xylene employed as starting material, is set forth in Table C below.

TABLE 0 Furnace Temper Pressure (in mm. Percent of Example ature, C. Hg) Poly(p-xylylene) recovered VIII 650 0. 4 4 IX 700 0. 3 26 X 700 O. 2 20 XI. 700 0. 04 35 Although it may be possible to employ a starting compound having the general structure id The fluorinated p-xylylene compounds which can be employed in the instant invention can also be expressed by the general structure wherein Y is a halogen having a lower bond strength than fluorine, Y is a member selected from the group consisting of hydrogen and halogens having a lower bond strength than fluorine, and n is an integer having a value of either 1 or 2.

These fluorinated p-xylylene compounds can be prepared from known a,u,u,a-tetrafluoro-p-xylenes by halogenation of u-tetrafluoro-p-xylenes. Halogenation of these fluorinated p-xylylene compounds is conveniently accomplished by introducing a haolgen subst-ituent having a lower bond strength than the fluorine already present in the alpha positions. For example, when cc,oc,ot',oc' tetrafluoro-p-xylene is employed, halogens such as chlorine, bromine, or iodine can be employed in the Y and/ or Y positions since they have lower bond strengths than fluorine.

When the a-perfluoro-p-xylene having the structure wherein n has a value of two and Y and Y are as above, are utilized they can be conveniently prepared from 1,2- bis a,a-difluoro-p-tolyl) tetrafluoroethane, by oxidizing 1,2- di(p-tolyl)tetrafluoroethane in a solution consisting of acetic acid, acetic anhydride and a strong mineral acid. This solution is then cooled to a temperature of between about 0 C. to 10 C. To the cooled solution is slowly added an oxidizing agent. Normally, any oxidizing agent may be used which is capable of oxidizing the 1,2-di(ptolyl)tetrafiuoroethane to the aldehyde stage. Generally, tertiary butyl chromates, chromium trioxide, and the like are satisfactory oxidizing agents for this purpose.

The oxidized solution is then poured into ice water and the resultant product is isolated by filtration, Washed with water and dissolved in an organic solvent from which it can then be recrystallized.

Recrystallization of the solute from the organic solvent will yield 1,2-bis(u,a-diacetoxy-p-tolyl)tetrafluoroethane.

The 1,2-bis a,a-diacetoXy-p-tolyl) tetraflu oroethane is then fluorinated to obtain l,2-bis(u,o-difiuoro-p1tolyl) tetrafluoroethane. This is accomplished by mixing it with sulfur tetrafluoride and heating. The resulting product is then dissolved in methylene chloride, washed with water and dried. Evaporation of the solvent yields l,2-biS(zx,udifluoro-p-tolyl)tetrafiuoroethane which is further purified by recrystallization from an organic solvent in the same manner as described immediately hereinabove.

The 1,2-bis(u,a-difluoro-p-tolyl)tetrafiuoroethane can now be halogenated in the same manner as described hereinabove. These halogenation reactions have been found to proceed Well when a mixture of either of the above pxylene compounds, a halogenating agent, such as gaseous chlorine, N-bromo-succinimide, and the like, and a suitable inert organic solvent are irradiated with ultraviolet light while the mixture is maintained at the reflux temperature of the solvent. However, it should be understood that, while this halogenating process is preferred, other halogenating techniques can also be successfully employed.

In accordance with the process of the instant invention, substantially improved yields of reactive intermediary p xylylenes having the general structure can be obtained from fluorinated p-xylene compounds having the general structure wherein Y, Y and n are as described hereinabove, when tural formula F fill-@01 2 l I F 2CC F 2 are produced.

While the reactive intermediary p-xylylenes having the general structure are obtainable in accordance with the general process described immediately hereinabove, it has been found that even higher yields of these reactive intermediary p-xylylcues are realizable when an inert diluent, such as those which have been described hereinabove, is employed.

Furthermore, condensation of the reactive intermediary p-xylylenes to form the oc-octafluoro-di-p-xylylenes is materially facilitated through the use of an inert diluent. When an inert diluent is not utilized, such condensation, although feasible, must be very closely regulated permitting very, little variance in control conditions. Without an inert diluent, it is also necessary to employ additional steps in the condensation process before dimerization of the reactive intermediary p-xylylenes to u-octafluoro-di-pxylylene can be realized. Use of such diluent is therefore preferred. Hence, the starting compounds having the general structure wherein Y, Y and n are as described hereinabove, can be heated, in contact with a metal reducing agent and an inert diluent, at the temperature ranges employed herein to obtain even higher yields of reactive intermediary pxylylenes from which greater amounts of tx-octafluoro-dip-xylylenes are realized.

Whenever an inert diluent is employed, it is essential that the condensation of the resulting reactive intermediary p-xylylenes to form a-octafluoro-di-p-xylylenes be accomplished in the presence of an organic solvent. In order to remove the residual heat from the hot reactive intermediary p-xylylene vapors without distilling or vaporizing the organic solvent, it is preferred that the reactive intermediary p-xylylenes be cooled to about 200-400 C., but at temperatures above the ceiling condensationpolymerization temperature of the reactive intermediary p-xylylenes. Cooling to below the ceiling condensation temperature, in the absence of the organic solvent, will cause almost spontaneous polymerization of the reactive intermediary p-xylylenes into poly(x-perfiuoro-p-xylylene). This ceiling condensation temperature is generally between 25 C. and 200 C. depending somewhat on the pressure. However, when in the vaporous state, the reactive intermediary p-xylylenes are relatively stable and do not polymerize.

The cooling of these hot reactive intermediary p-xylylene vapors can be accomplished in accordance with any one of several convenient means. For instance, internal or external condensers, cooling coils, tubes or the like can be employed immediately after the reduction chamber, or, if desired, natural cooling created by long runs of air- 12 cooled tubing or pipe from the reaction chamber to the condensing medium can be used. It is also possible to mix an organic solvent condensing medium in the vapor state with the hot reactive intermediary p-xylylene vapors in a suitable manner or by mixing directly in the chamber as another method.

It is essential in this condensation process that the cooled vaporous reactive intermediary p-xylylenes be conducted in the presence of a fluid medium of an inert organic solvent. Organic solvents which have been found suitable for this purpose are those such as p-xylene, benzene, toluene, o-xylene, rn-xylene, cumene, methylnaphthalene, o-dichlorobenzene, 1,2-di-p-tolylethane, mineral oil, diphenylmethane, 1,2-diphenylethane, heptane, decahydronaphthalene, and the like and preferably those having an atmospheric boiling point of between about 50 C. and 350 C.

The resulting a-octafluoro-di-p-xylylene product forms upon condensation of the vaporous reactive intermediary p-xylylenes in the presence of the fluid medium. It is not essential, however, that the fluid medium be in the liquid state. While this is most desirable, condensation can be accomplished equally as well by mixing the hot reactive intermediary p-xylylene vapors with a vaporous organic solvent and then simultaneously condensing the total mixture to the liquid state for recovery.

When the cooled vapors of the reactive intermediary p-xylylenes are collected in a liquid medium, merely 'bubbling or dispersing the vapor below the liquid level of the organic solvent is an adequate means by which these pxylylenes may be caused to dimerize to the a-octafluorodi-p-xylylenes and be subsequently recovered from the solvent solution. The bath into which these vapors are condensed may be maintained at any temperature above 50 C. but preferably between a temperature of from 50 C. to 250 C.

Bath temperatures below 50 C. are considered undesirable and burdensome to maintain. The heat of condensation and cooling given off by the hot reactive intermediary p-xylylene vapors act to conveniently maintain the organic solvent at temperatures above about 50 C. It has been found that conversion of the reactive intermediary p-xylylenes to the polymer is increased when the bath temperatures fall below about 50 C. Therefore, to avoid competing reactions and decreased yield of the cyclic dimer, it is considered preferable to maintain the temperature of the bath between about C. and 250 C. Thus, when employed herein, the term fluid media is intended to cover both the liquid or gaseous state of the solvent medium in which the hot reactive intermediary p-xylylene vapors are collected.

Recovery of a-octafiuoro-di-p-xylylene is relatively simple. It can, for instance, be readily recovered by subliming it from high boiling solvents such as mineral oil. Preferably, however, a desirable method is to remove a majority of the lower boiling solvent medium by distillation and then crystallize the a-octafiuoro-di-p-xylylenes from the remaining solvent by cooling and filtering off the crystallized a-octafluoro-di-p-xylylenes, although other recovery techniques can also be successfully employed.

In a preferred embodiment of this invention, an ct-tetrafluoro-p-xylene having the structure wherein n has a value of either one or two, Y is a halogen having a lower bond strength than fluorine and Y is a member selected fro-m the group consisting of hydrogen and halogens having a lower bond strength than fluorine, is added to a mixing zone wherein it is mixed with steam and passed through a reaction chamber. The reaction chamber is packed with copper mesh and maintained at temperatures of between about 400 C. and 800 C. The

hot reactive intermediary p-xylylene vapors which form are cooled in a condenser at the outlet of the reaction chamber to a temperature of between about 150250 C. in order to isolate the cuprous halide compound which forms. The reactive intermediary p-xylylene vapors are then passed into a hot organic solvent bath which is maintained at temperatures of from between about 80-90 C. by the hot vapors of the reactive intermediary p-xylylenes wherein these reactive intermediary p-xylylenes condense to form the cyclic dimer, a-octafluoro-di-p-xylylene.

Either continuously or in stages, the aqueous layer of the condensation medium is remomed and the solution concentrated by flashing or reduced pressure distillation to about one-tenth its original volume. Upon cooling, the a-octafluoro-di-p-xylylenes, which have crystallized from the organic solution in high purity, are then separated from the mother liquor by filtration or by centrifugation, washed and dried.

Examples XILXVIII are set forth below as illustrative of the manner in which ot-octafluorddi-p-xylylenes may be obtained in accordance with the process of the instant invention. Unless otherwise specified, all parts are by weight.

EXAMPLE XII A 5.58 gram sample of a,a'-dibromo-a,a,M i-tetrafluoro-p-xylene was metered into a reaction chamber along 370 grams ofwater, the water having been previously purged of oxygen by nitrogen over a period of one hour. The reaction chamber was maintained at a temperature of 700 C. and packed with 24 grams of copper mesh. The efiiuent vapors of Ot-lIGtTELfiHOI'O-P-XYIYICHC, which subsequently formed, were quenched by passing them into a 2,000 milliliter 3-neck flask containing 1500 milliliters of toluene. The toluene was maintained at a temperature of about 84 C. The 3-neck flask was fitted with a bottom take-off in order to remove the excess water. Upon completion of the passage of the steam mixture of r,a-dl bromo-a,a,a',m-tetrafluoro-p-xylene, methyl chloride was used to thoroughly wash the apparatus and these washings were added to the toluene quench solvent. The organic solvent and aqueous fraction were then filtered to remove any insoluble copper salts and polymer which might be present. The organic solvent was next extracted twice with by volume, hydrochloric acid while the aqueous portion obtained from the 3-neck flask was extracted once with methylene chloride. Next, the combined organic solvents were concentrated to yield 0.726 gram of a pale yellow solid which, upon tri-turation with n-hexane, yielded 0.246 gram of a-octafiuoro-di-p-xylylene. Vapor phase chromatography of the hexane filtrate indicated that or 0.096 gram, of the solid mixture was cyclic dimer. The total amount of the cyclic dimer obtained was 0.342 grams which resulted in a final yield of 11.7%.

The filtered solid which contained the copper salts and polymer was washed thoroughly with dilute hydrochloric acid to remove cuprous bromide. This was followed by a thorough washing with acetone to remove cupric bromide and water. There remained 0.13 gram of a solid whose infrared spectrum showed it to be-identical with poly(a-tetrafluoro-p-xylylene) EXAMPLES XIII-XVIII The same procedure was followed as in Example XII above except that the amounts of a,et'-dibromo-a,a,a',a'- tetrafluoro-p-xylene and the temperatures in the reaction chamber have been varied. The amount of water used has also been varied depending upon the amount of starting material employed.

Examples XIILXVIII are tabulated and set forth in Table D below wherein the amount of a,ot'-dibromo-a,a, a,a'-tetrafluoro-p-xylene employed as starting material is designated under the column headed Dibromo and the column indicating percentage of yield refers to the yield of a-octafluoro-di-p-xylylene obtained.

While the process described immediately hereinabove has been directed specifically to obtaining u-octafluoro-dip-pxylylene, it is currently believed that similar methods could not be utilized .to obtain a-octachloro-di-p-xylylene, a-octabromo-di-p-xylylene and/or a-octaiodo-di-p-xylylene. This belief stems from the fact that substitution of the hydrogen atoms in the at positions of the reactive intermediary p-xylylenes with larger atoms; such as those of chlorine, bromine and/ or iodine, decreases the tendency to form these u-halogenated cyclo-di-p-xylylenes due to steric hindrance.

While it may be possible to substitute the chlorine atom for the hydrogen atom in the Ot-pOSltiOl'lS of a cyclo-di-pxylylene, it is not deemed to be feasible to similarly substitute either the bromine atom or the iodine atom. Although it is still to be achieved, such substitution with chlorine might be feasible due to its atomic size when compared to that of the fluorine atom. However, similar substitution with either bromine or iodine is seriously doubted due to the significant diiferences in their atomic size when compared to that of fluorine and chlorine but particularly with that of fluorine. These differences in atomic size are deemed to give rise to such steric hindrance as to render obtaining the theoretical structure of either a-octa-bromo-di-p-xylylene or a-octaiodo-di-p-xylylene highly improbable.

Although the above discussion has been directed to the feasibility of substituting either chlorine, bromine or iodine atoms in lieu of fluorine atoms for the hydrogen atoms in the OL-POSllZlOIlS of a cyclo-di-p-xylylene, and sets forth the current prevailing theory regarding such substitution, it should be understood that the applicant in no way intends to be bound or limited to said theory or belief.

While the invention has been described in detail and with particularity, it should be understood that the processes, methods and limitations set forth herein may be altered and modified without departing from the scope and spirit of the invention as contained in the appended claims.

What is claimed is:

1. A process for the preparation of p-xylylene-containing compositions which comprises forming reactive intermediary p-xylylenes having the general structure wherein Y is a member selected from the group consisting of halogens, hydrogen and mixtures thereof, by heating, in contact with a metal reducing agent and at a temperature of between about 400 C.800 C., a compound having the general structure wherein Y is a member selected from the group consisting of halogens, hydrogen and mixtures thereof, X is a member selected from the group of halogens having a bond strength no greater than that of Y, Z is a member selected from the group consisting of hydrogen and halogens having a bond strength no greater than that of Y, and n-is an integer from 1 to 2 inclusive, with the proviso that when n has a value of 2, Y is a member selected from the group consisting of all halogens and hydrogen, and thereafter condensing the thus formed intermediary p-xylylenes to obtain said p-xylylene-containiug compositions.

2. The process of claim 1 wherein the metal reducing agent is a member selected from the group consisting of copper, zinc, aluminum and tin.

3. The process of claim 1 wherein an inert vaporous diluent is employed.

4. The process of claim 3 wherein the inert vaporous diluent is steam.

5. A process for the preparation of p-xylylene-containing compositions which comprises forming reactive intermediary p-Xylylenes having the general structure wherein Y is a member selected from the group consisting of halogens, hydrogen anl mixtures thereof, by heating, at a temperature of between 400 C.800 C. in contact with copper and steam, a compound having the general structure xtvioorrl z wherein Y is a member selected from the group consisting of halogens, hydrogen and mixtures thereof, X is a member selected from the group of halogens having a bond strength no greater than that of Y, Z is a member selected from the group consisting of hydrogen and halogens having a bond strength no greater than that of Y, and n is an integer from 1 to 2 inclusive, with the proviso that when n has a value of 2, Y is a member selected from the group consisting of all halogens and all hydrogen, and thereafter condensing the thus formed intermediary p-Xylylenes to obtain said p-Xylylene-containing compositions.

6. A process for the preparation oi poly(p-Xylylenes) which comprises:

(a) heating, in contact with a metal reducing agent and at a temperature of between about 400 C.800 C., a compound having the general structure wherein Y is a member selected from the group consisting of halogens, hydrogen and mixtures thereof, X is a member selected from the group consisting of halogens having a bond strength no greater than that of Y, Z is a member selected from the group consisting of hydrogen and halogens having a bond strength no greater than that of Y, and n is an integer from 1 to 2 inclusive, with the proviso that when n has a value of 2, Y is a member selected from the group consisting of all halogens and all hydrogen, to form reactive intermediary p-Xylylenes having the general structure wherein Y is a member selected from the group consisting of halogens, hydrogen and mixtures thereof;

(b) isolating the metal halide compound formed during heating by depositing said metal halide compound on a surface which is maintained at a temperature above the condensation temperature of the reactive intermediary p-xylylenes;

(c) condensing the vapors of said reactive intermediary p-Xylylenes on a surface which is at a temperature below the condensation temperature of the reactive intermediary pxylylenes to recover poly(p-xylylenes).

7. The process of claim 6 wherein the pressure during heating is between about 0.01 mm. Hg-l mm. Hg.

8. The process of claim 6 wherein the surface upon which the metal halide compound is deposited is at a temperature of between about 150 -850 C.

i ii 9. The process of claim 6 wherein the surface upon which the reactive intermediary p-xylylenes are condensed is at a temperature of between about 30 C.- C.

10. A process for the preparation of stable p-Xylylenes which comprises: i

(a) heating, in contact with a metal reducing agent and at a temperature of between about 400 C.800 C., a compound having the general structure wherein Y is a member selected from the group consisting of halogens, hydrogen and mixtures thereof, X is a member selected from the group consisting of halogens having a bond strength no greater than that of Y, Z is a member selected from the group consisting of hydrogen and halogens having a bond strength no greater than that of Y, and n is an integer from 1 to 2 inclusive, with the proviso that when n has a value of 2, Y is a member selected from the group consisting of all halogens and all hydrogen, to form reactive intermediary p-Xylylenes having the general structure wherein Y is a member selected from the group consisting of halogens, hydrogen and mixtures thereof;

(b) isolating the metal halide compound formed during heating by depositing said metal halide compound on a surface which is maintained at a temperature above the condensation temperature of the reactive intermediary p-Xylylenes;

(c) passing the vapors of said reactive intermediary p-xylylenes into a cold organic solvent which is maintained at a temperature of below about -40 C; and

(d) recovering p-Xylylenes from the cold organic solvent and maintaining said p-Xylylenes under an inert atmosphere which is at a temperature of below about 40 C.

11. The process of claim 10 wherein the surface upon which the metal halide compound is deposited is maintained at a temperature of between about 150C.350 C.

12. A process for the preparation of a-oct-afluoro-di-pxylylenes which comprises:

(a) heating, at a temperature of between about 400 C.800 C. in contact with a metal reducing agent and an inert diluent, a compound having the general structure wherein Y is a member selected from the group consisting of halogens having a lower bond strength than that of fluorine, Y is a member selected from the group consisting of hydrogen and halogens having a lower bond strength than that of fluorine, and n is an integer from 1 to 2 inclusive, to form a reactive intermediary a-tetrafiuoro-p-xylylene compound;

(b) quenching the vapors of said reactive intermediary in an inert organic solvent which is maintained at a temperature of above about 50 C.;

(c) and thereafter recovering said ,a-octafluoro-di-pxylylenes.

13. The process of claim 12 wherein the inert diluent is steam and is present in an amount of between about 40:1 to :1 parts by weight of inert diluent to the compound having the general structure References Cited by the Examiner UNITED STATES PATENTS 9/1962 Davis et a1. 260666 9/1964 Poilart 260-670 References Cited by the Applicant L. A. Errede and B. F. Landrum: J. Am. Chem. Soc. 79, 4952 (1957).

18 E. Muller and I. Muller-Rodlotf: Annalen, 1935, 517, 134.

D. S. Acker et al.: J. A. Chem. Soc. 82, 6408 (1960). M. Ballester and J. Castaner, Annales de Fisica y 5 Quimica 207, (1960.)

W. R. Hartler: J. Org. Chem. 28, 2877 (1963). M. Labes et al.: J. Chem. Phys. 33, 868 (1960). L. R. Melby et al.: J. Am. Chem. Soc. 84, 3374 (1962). G. Briegleb: "Elektronen-Donator-Acceptor K-ornplexe,

10 Springer-Verlay, A. G. Berlin, 1961, p. 37.

L. A. Errede, R. S. Gregorian and J. M. Hoyt: J. Am. Chem. Soc., 82, 5218 (1960).

DELBERT E. GANTZ, Primary Examiner.

G. E. SCHMITKONS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 280 202 October 18 1966 Heinrich G. Gilch It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 14, lines 74 and 75, before "hydrogen" insert all Signed and sealed this 5th day of September 1967,

(SEAL) Attest:

ERNEST W. SWIDER Attesfing Oifioer EDWARD J. BRENNER Commissioner of Patents 

1. A PROCESS FOR THE PREPARATION OF P-XYLYLENE-CONTAINING COMPOSITIONS WHICH COMPRISES FORMING REACTIVE INTERMEDIARY P-XYLYLENES HAVING THE GRNERAL STRUCTURE 